Researchers in South Africa have learned something new about how antibodies fight off HIV in research that could advance the quest to develop a vaccine against the virus.

In a paper published online Sunday in Nature Medicine, researchers from the Centre for the AIDS Programme of Research in South Africa tracked how the evolution of the virus in two infected woman shaped the antibodies they produced to fight it. Several months after infection, the researchers saw that the patients had developed more "broadly neutralizing antibodies," which target different versions of the virus.

One of the women had neutralized 88 percent of 225 HIV virus subtypes after three years with the virus, while the other woman had neutralized 46 percent of 41 subtypes after two years of infection.

The researchers found that a specific change in the coating of the HIV virus appeared to be the trigger for the women to produce antibodies that could thwart its entry into cells.

One reason the HIV virus has proven so difficult to fight is that it is skilled at hiding from antibodies that can block the virus from attacking cells. But researchers believe that the more they understand how the antibodies develop, the better chance they have at developing an HIV vaccine.

Now, the South African researchers write, it's clear that there's a "dynamic interplay early antibodies and viral escape" that can determine the immune system's ability to keep the virus at bay.

As Richard Knox reported this summer, researchers are also hopeful about making a vaccine that would prime the immune system to mop up infected HIV cells after a drug forces the virus out of the cells.

And earlier this year, researchers reported in Nature that an experimental vaccine protects monkeys against infection with a virus that is very similar to HIV. In that trial, researchers learned that a successful vaccine will have to aid the immune system in making antibodies against a specific part of the virus's envelope, or outer coating, called the V2 loop.

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